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## PowerPoint Slideshow about 'SENDER A.M. Transmitters' - barry-witt

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SENDER S.A.

- Company was created in 1997 by a group of engineers and
- technitians with long experience in Solid state A.M.
- Transmitters.
- Located in Santiago Chile, with 25 employes.
- 40% of them are shareholders.
- Main activity: Design and manufacturing of A.M. transmitters,
- antenna tuning units, duplexers and triplexers.
- First transmitter in operation Nov 1997.
- Transmitters sold up to now:127 from 1 KW to 12.5 KW.

Product Line

AM 1500 SS 1.5 KW/1.1 KW, single phase / 2 power

amplifiers

AM 3000 SS 2.25 KW/3KW, single phase or 3 phase / 4 power amplifiers.

AM 7500 SS 5.5 KW/ 7.5 KW, 3 phase or single phase / 7 power amplifiers.

AM 15000 SS 11 KW/13 KW,3 phase / 14 power amplifiers

AM 25000 SS 22 KW/26KW, 3 phase / 28 power amplifiers

A.T.Us for 1.5 KW, 3 KW,7.5 KW, 13 KW and 26 KW

Product highlights

- Solid State. Modular / redundant
- architecture
- High efficiency. PWM & class D R.F.
- amplifiers
- Hot plug in power amplifiers with Mosfets.
- Simple design with standard components.
- Totally rustproof cabinet made of iridated
- aluminum with stainless steel hardware.
- Excellent specs and audio quality.
- Outstanding factory support.
- Very competitive price.

Basic specifications

Frequency range: .53 MHZ to 1.7 MHZ.

Input voltage: 110V or 220 V single phase, 220V or 380V 3 ph

+or - 10%. Line frequency 47HZ to 63 HZ.

Efficiency: 75% or better for single phase transmitters,

80% or better for 3 phase transmitters.

Frequency response: Better than +or- 1 dB 30 Hz to 10 KHZ.

Distortion: Less than 1% at nominal power and 90% modulation.

Harmonics and spurious:- 73 dB or better for AM 1500 SS,

- 80 dB or better for other models.

Frequency stability:+- 5 Hz.

Output impedance: 50 Ohm

Dimentions and weigths:

AM 1500 SS W=44 cm,H=62.5cm

D=60 cM , 100 Kg.

AM 3000 SS W=44 cm,H=65.5cm

D=60 cM , 160 Kg.

AM 15000 SS W=80 cm,H=181cm

D=81 cM , 500 Kg.

Standard features:

2 power level with independient adjustment

and modulation autotracking.

Start, stop,power level selection and power

level adjustment remotely controled.

Automatic alarm reset.

Positive and negative limiter.

Relationship with RICHARDSON ELECTRONICS

- Exclusive representation for Asia and other specific countries.
- Joint project to manufacture transmitters in U.S.A.
- Sender sells Omnicast F.M. Transmitters in Latin America.
- Excellent level of personal contacts .

Near future projects

- FCC type acceptance.
- Frequency agile 1.5 KW transmitter.
- IBOC compatibility.
- Inboard audio processor and modulation monitor.
- Higher power amplifiers

Reliability in A.M. stations

Introduction

- Harmonic set of:
- Transmitter
- Radiating system
- Energy System
- Auxiliary Equipment

Station Concept

Experience with stations using Solid State A.M. Transmitters

- Very high reliability if precautions related with the following topics are considered:

Antenna discharges

A.C. Source transients and discharges

A.C. Source voltage limits

Load stability

Interference from nearby stations

Reliability is reduced in unprotected stations

STL

RX

ATU

TX

Basic elements of a stationANTENNA

Audio &

Rem. Ctrl.

RF

H.V

TRANSF.

DISTR.

BOARD

T.P.

A.C.

GROUND PLANE

TRANSMITTER BASIC BLOCKS

- POWER SUPPLY
- PWM MODULATOR
- R.F. DRIVER
- CLASS D or E
- R.F. OUTPUT FILTER
- CONTROL,PROTECTIONS,SIGNALING
- EXTERNAL INTERFACE

PWM MODULATOR

- GENERATES D.C + A.C. VOLTAGE FOR THE R.F. AMP.
- SWITCHING DEVICE, HIGH EFFICIENCY
- A FILTER IS NEEDED TO ELIMINATE SWITCHING FREQUENCIES
- CONMUTATION FREQUENCY IS 72 KHZ.

PWM (PULSE WIDTH MODULATION)

SIMPLIFIED DIAGRAM:

R.F.

AMPLIFIER

D.C. SUPPLY

Switch

(Mosfet)

PWM FILTER

LOAD

PWM waveform

Filtered output voltage

1)

2)

S

3)

V

RL

4)

PWM BASIC OPERATION- Between 1) y 4) duty cycle is increased
- Mean voltage in the load increases proportionally
- A filter is required to remove high frequency components

F = 72 kHz

PWM Frequency spectrum

Amplitude

D.C. component

PWM 180°

Audio

72 KHZ components out of phase

Frecuency

144 kHz

72 kHz

Load change consequences

- With reduced load (Rload< Rnominal) transmitter will produce high frequency submodulation
- With increased load (Rload>Rnominal) transmitter will show high frequency overmodulation
- Distorsion will increase if filter is not propperly loaded.

Cgd

Cgd

Cgd

Cgd

Cds

Cds

Cds

Cds

Cgs

Cgs

Cgs

Cgs

Class D Bridge parasitic elementsV+

RL

Ciss = Cgs + Cgd

Crss = Cgd

Coss = Cds + Cgd

R.F. drive circuit

- Ls and Cs series resonant
- Lp paralel resonant with mosfet input capacitance (Partially)

Ls

Cs

MOSFET drive

Drive signal

Lp

SCgs

Class D Amplifier basics.

- Low impedance driver required for:
- Fast switching
- Low Vgs modulation by Crss
- Tuned load to produce sinusoidal current
- High efficiency (>95 %)
- Duty cycle should be < 0.5
- Avoid transversal currents
- Coss charge and discharge through Rl

MOSFET characteristics

- No secondary breakdown
- positive temperature coeff. Of Rdson (Simplify parallel operation)
- Voltage controled device (Vgs)
- Driver impedance dependent switching times.
- Intrinsic antiparallel diode

IRFP350 MOSFET

- Rdson = 0.3 ohms
- Vdss = 400 Vdc
- Vgs = +/- 20 Vmax Vth = 3 V Vsat = 9 V
- Id = 16 A @ Tc=25ºC 10 A @ Tc=100ºC
- Idmax = 64 A
- Capacitance @ f=1MHz, Vds=25V , Vgs=0V
- Ciss = 2600 pF (2400 pF for Vds>40V)
- Coss = 660 pF (200 pF for Vds>40V)
- Crss = 250 pF (50 pF for Vds>40V)

Cicuit data

Vdc = 110 V

F = 1600 kHz

d = 0.43

Transistor IRFP350

Rdson = 0.3 ohms

Ton = 16 ns

Toff = 40 ns

Coss = 200 pF

L2 = 7.04 uH

C2 = 1.55 nF

Operational data

RL = 15 ohms

Po = 132.36 W

h = 97.93 %

Transistor stresses

Vmax = 110.81 V

Imax = 4.12 A

Pdis = 0.70 W x2 (1.4 Wtotal)

SENDER

Class D Simulation(1/2 bridge,Vmax<400x.75/2.5)*Simulated with HB plusfrom Design Automation

Class E amplifier basics.

- R.F.Choke large enough to produce constant current
- High Q series resonant circuit to produce sinusoidal current
- Vds y dVds/dt =0 prior to starting conduction
- High efficiency (>95%)
- if special high voltage transistors with low Rdson are used

Circuit Data

Vdc = 33 V

F = 1600 kHz

d = 0.48

Transistor IRFP350

Rdson = 0.3 ohms

Ton = 16 ns

Toff = 40 ns

Coss = 200 pF

L1=12.3uH L2=3.7uH

C1= 4.1nF C2=4.9nF

Operational Data

RL = 7.3 ohms

Po = 125.27 W

h = 90.53 %

Transistor stresses

Vmax = 118.79 V

Imax = 9.84 A

Pdis = 6.55 W x2 (13.1 Wtotal)

SENDER

Clase E Simulation(Vmax<400x.75/2.5)*Simulated with HEPA Plus from Design Automation

Passband Output filter

- Reduce R.F. Harmonics
- High third harmonic att > 80 dB
- Medium second harmonic att. > 40 dB
- Higher harmonics att > 70 dB
- Permits impedance matching between amplifier and load.
- Atenuates low frequency components (Lightning protection)

Output filter

- Design oriented to protect R.F.amplifier
- Low frequency attenuation
- Inductor input
- Strategically located sensors:
- Spark Gap °Transient suppressor
- SWR °Overpower
- Overcurrent °Phase
- Input transient suppressor(Active or pasive)

Posible Transmitter Agresions

- Antenna
- Impedance change and discharges
- A.C. Supply
- Voltage variation and transients
- Program signal
- Level variations and transients
- Ground
- Transfered potentials and high ground currents

Antenna related problems

- Impedance change
- Low heigth antennas are particularly unstable
- Restricted bandwidth
- Interference from other stations
- Discharges

A.T.U.Sensibility to antenna impedance changes

Change in XL (+/- 10 ohm=6%)

if ZL=8-j150 Zin=19.5-j24.4 SWR=3.26

if ZL=8-j160 Zin=50+J0 SWR=1

if Zl=8-J170 Zin=19.5+j24.4 SWR=3.26

Change in RL ( +/- 1 ohm =12.5%)

if ZL=7-j160 Zin=57.1+j0 SWR=1.14

if ZL=9-j160 Zin=44.4+j0 SWR=1.14

RL and XL simultaneous variation

if ZL=7-j150 Zin=18.8-j26.8 SWR=3.52

if ZL=7-j170 Zin=18.8+j26.8 SWR=3.52

if ZL=9-j150 Zin=19.9-j22 SWR=3.10

if ZL=9-j170 Zin=19.9+j22 SWR=3.10

!

Complex A.T.U. (dual T)-j44.9

j50.5

j5

j145

Zin

50+j0

ZL

8-j160

20-J13

-j92.5

j37

-20°

20°

Variations in XL

if ZL=8-j150 Zin=50+j62.5 SWR=3.26

if ZL=8-j160 Zin=50+j0 SWR=1.00

if ZL=8-j170 Zin=50-j62.5 SWR=3.26

Note: SWR of 8+/-j10 refered to a 8+j0 is 3.26

Load ladder

RF amplifiers

50 Ohm

Antenna

Z1

1

combiner

A.T.U.

filter

Zn

n

15 Ohm

Extreme values for SWR 1:1.5, refered to 50 Ohm, are:

33.3+j0 75.0+j0

50-j20.4 50+j20.4

A.T.U. And amplifier stresses

A)ZL=50-J62.5

Eff=93.5% Po=4.5W Ip=15.5A

B) ZL=50+J62.5

Eff=90.9% Po=2.02W Ip=1A

C) ZL=19.5+J24.4

Eff=84% Po=44W Ip=105A

D)ZL=19.5+J24.4

Eff=93.8% Po=395W Ip=73.7A

20°+20°

90°

Atmospheric discharges

- At the antenna
- In A.C.lines
- In telephone lines

Characteristics

Imax: 200 kA Itypical: 10 a 20 kA

dI/dT typical: 10 kA/useg

Risetime: 2 useg Decay time:40 useg to 50%

Criteria to minimize damages

- Disipators
- Avoid charge acumulation using sharp points
- or active systems
- Well designed grounding system
- Low impedance direct paths
- High impedance undesired paths
- Radial equipotential conections
- Antenna and ground conection closely located at TX

Discharge probability function

N = 15 L (C·H+h)2 ·10-6

N = Discharges per year

L = Ceraunic level (Nº of days per year when thunderstorms are heared)

C = Site topographic index (0 to 0,3)

H = Site mean heigth above surroundings (1 to2 km)

h = Antenna heigth

Example: C=0.1 L=50 H=100m h=120m

N = 12.7 discharges per year.

Discharge current circulation

17

1

3

2

1. Strike

2. Antenna

3. Discharge through the antenna

4. Guy

5. Isolator

6. Spark gap

7. Ground rod

8. Base insulator

9. Cnecting Loop

11. A.T.U. isolator

12. A.T.U.

13. Ferrite core

14. Coaxial cable

15. Discharge current in caxial cable

16. A.T.U. Spark gap

17. Disipator

4

9

15

13

14

12

11

5

6

16

8

7

10

Equipment Instalation

Reference ground

Coaxial cable

A.C. Line transient protector

A.C. mains

Panelboard

Ferrite toroids

Ground to auxiliary equipment

Transmitter A.C. line

Building ground

Interference

1.- Intermodulation products are generated

2.- SWR protection is desensitized

3.- Dangerous voltages at the R.F. Amplifier and

output filter maybe generated.

Transmitter Protections

- A.C.input
- Overload
- Short cicuit
- Transients
- Overvoltage
- Undervoltage
- Assimetry
- D.C.supply
- Overload
- Transients
- Failure

- R.F.
- Overcurrent
- SWR
- Phase
- overpower
- Transients
- Internal
- R.F. Drive Temperature
- PLL

Factory tests to ensure transmitter reliability

- Power amplifiers
- Long time operation at 150% modulation
- Output
- Open cicuit
- Short circuit
- Simulated lightning strike
- SWR
- A.C. input
- Phase failure
- Simulated transient
- Voltage variationSENDER

Conclusions

Reliability in a transmitting sytem is a function of:

- Transmitter intrinsic reliability
- Power stages regimes much lower than devices limits
- Simple low power stages with low number of components
- Rational protections adjustment

Conclusions

- High quality station engineering
- A.C. Transient protection
- Antenna discharges protection
- Well dimentioned and coordinated grounds.
- Stable radiating sysytem.
- Interference filtering
- Coordination with the manufacturer

Recomended instrumentation for test and adjustment

- 1.- To measure resonance:
- 1.1 R.F.Generator
- 1.2 Oscilloscope or spectrum analyzer
- 2.- To measure R.F.impedance:
- 2.1 R.F. bridge (General Radio 1609 or Delta OIB-3)
- 2.2 R.F. generator (Delta RG3-A or similar)
- 2.2 Spectrum analyzer (HP 8553B or similar) or detector included in RG3-A

- 2.3 An H.P. vector impedance meter
- may be used instead of 2.1,2.2 and 2.3

- 3.- To measure power:
- 3.1 R.F. Dummy load,non inductive or with
- a tuning network to adjust it to 50+J0 Ohm.
- 3.2 R.F. Ammeter (Delta TC-1 or similar)
- or R.F. Wattmeter
- 4.- To measure frequency response and distortion:
- 4.1 General purpose oscilloscope, 2 channel 4.2 Audio analyzer (Audio precision Portable
- One or similar)
- 4.3 Modulation monitor (H.P. 8901 A or B , Belar AMM3, TFT 923 A.M. or similar.)

- 5.- To measure spectrum.-
- 5.1 Spectrum analyzer 100KHZ.to 50 MHZ or more
- TEK 2711, H.P. 8553B plus display unit or similar).
- 5.2 R.F. atenuator.
- 5.3 OPTIONAL. Notch filter to remove the carrier
- frequency and avoid intermodulation
- 6.- To check efficiency.
- 6.1 A.C. Analyzer.(To measure A.C. voltage, current,
- power and power factor

- 7.- To measure transmitter carrier frequency.
- 7.1 Digital frequency meter up to 10 MHZ.
- Or higher frequency, time base 1 P.P.M. or less.
- 8.- To measure temperature.
- 8.1 Infrared temperature measuring unit with suitable digital multitester. (Fluke).
- 9.- For general voltage and current measurements:
- 9.1 True RMS digital multimeter, suitable to operate in high R.F. fields. (Our best experience is with Fuke Digital multimeters.)

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